For instance, the BP2,153,328 discloses such a packaging apparatus in its proper specification and accompanying drawings, which features the structure capable of executing those steps including the following; a step to convey a number of tray-form containers each containing food product aligned in file at predetermined intervals; a step to tubulate a belt-form thermoplastic film being conveyed at a speed identical to that of those containers in the periphery of each container; a step to carry forward these containers and the tubular film further to the downstream side via rotation of a pair of side belts nipping each container from both sides; and a final step to cut off the tubular film between each container with a cutting means. Furthermore, the packaging apparatus disclosed in the above-identified BP2,153,328 pulls both ends of the cutoff tubular film in order to superpose the both ends by folding them onto the bottom surface of each container. After completing these steps, the film generates tension and promotes transparent look. This in turn favorably leads consumers to visually sense that food in each container is by far the fresh than normally being felt.
Nevertheless, since those food-containing packages internally contain substantial volume of air, food sealed in those packages is apt to rot as time goes by. Therefore, in order to prevent this, the above-identified BP2,153,328 proposes such a technique described below. A slender tubular nozzle with one-end being linked with a vaccum pump is inserted in a tubular film previously being tubulated by a tubulating means and conveyed in the longitudinal direction so that air remaining in each container and the tubular film can be eliminated therefrom. In this case, capability to fully seal both ends of the tubular film is extremely important. To satisfy this need, it is essential that a box-motion type sealing means be introduced. This sealing means reciprocates a pair of vertically disposed sealing bars in the longitudinal direction of the tubular film. When these sealing bars shift themselves in the direction identical to that of the tubular film, these sealing bars continuously transmit heat to the tubular film to melt it. However, when vacuum absorptive force transmitted via the tubular nozzle acts upon the interor of the tubular film, the tubular film contracts itself in the direction opposite from the shiting direction. As a result, those sealing bars cannot fuse appropriate position of the tubular film. Furthermore, because of the reciprocating movement of these sealing bars, clearance between these sealing bars and the downstream end of a pair of side belts nipping each container from both sides is variable, and therefore, each food container cannot properly be shifted to those sealing bars.